Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver halide photography (see, e.g., JP-A-8-25813 (“JP-A” means unexamined published Japanese patent application) and JP-A-11-321128). Moreover, this system has advantages over silver halide photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In the dye diffusion transfer recording systems, a colorant-containing heat-sensitive transfer sheet and a heat-sensitive transfer image-receiving sheet are superposed, and the heat-sensitive transfer sheet is heated using a thermal head with which heat generation can be controlled by electric signals. Thereby a colorant in the heat-sensitive transfer sheet is transferred to the image-receiving sheet to record image information. More specifically, a transferred color image with a continuous change in color shading can be obtained by recording three colors including cyan, magenta and yellow, or four colors including black in addition to the three colors in the manner of one over another.
Owing to a recent progress of computerized digital image processing technique, a quality of the recorded image is improving and a market of the dye diffusion transfer recording system is growing. In accordance with the growth of market, a demand for both speed-up of the print system and high density imaging is increasing.
In the heat-sensitive transfer image-receiving sheet of this system, a receiving layer dyeing the transferred colorant is formed on a support. It is also known that it is possible to improve the dye transfer efficiency by coating a heat insulation layer containing hollow particles on a support and thus utilizing the insulation effect of the voids in the hollow particles, and thus, proposed was a method of raising the density of transferred image further by forming two or more heat insulation layers containing hollow particles (see, e.g., JP-A-2006-62114 and JP-A-2007-264170).
Although the method is effective in increasing the density of the transferred image, the heat-sensitive transfer image-receiving sheet after printing was insufficient in resistance to so-called heat blurring, which means an image blurring when stored at relatively high temperatures. Further, surface irregularity was generated on the sheet during print conveyance by spike scars with the grip rollers that are in contact with the back side of the support. In this way, the method raised a new problem that defects of non-printing occurred in the area to be printed.
On the other hand, printers having a mechanism of holding a heat-sensitive transfer image-receiving sheet with grip rollers consisting of a rubber roller and a metal roller and conveying the sheet reciprocally by their revolution, which are simpler structurally, allow reduction in size and are cheaper, are used most widely (see, e.g., JP-A-11-115328).
In the case of such a printer, the grip rollers consist of a rubber roller for prevention of slipping of paper and a metal roller conveying the heat-sensitive transfer image-receiving sheet accurately by gripping it with fine protrusions (hereinafter referred to as “spikes”) having a height of about 40 to 100 μm formed on the surface by etching.
However, in the case where the heat-sensitive transfer image-receiving sheet has a layer mechanically brittle, the spike scars cause serious problems that defects of non-printing on the printed face occur.